Study explores the benefits of shunt surgery for patients with normal-pressure hydrocephalus

Typically affecting older adults, normal-pressure hydrocephalus (NPH) is one of the more-difficult conditions to diagnose. In addition to gait difficulty and incontinence, the symptoms include cognitive impairment, which is often characterized as memory loss.

The cause of enlarged ventricles, found on CT or MRI scanning, is uncertain. However, it has been shown experimentally to be associated with:

Decreased absorption of spinal fluid

Increased pulse pressure or systolic blood pressure (BP), or both

Brain atrophy

Mayo Clinic neurologists and neurosurgeons have a long experience in treating NPH and assessing factors that may predict outcomes.

Diagnosis and treatment

After other causes of gait disturbance have been ruled out, patients at Mayo have a test that mimics a temporary shunt to determine whether decreasing cerebrospinal fluid volume improves gait. Typically, 30 cc of fluid is removed during a spinal tap, and pre- and post-procedure videos of the patient walking are compared.

Separately, tests for cognitive function are conducted to help determine if memory problems are isolated or are accompanied by other impairments. The presence of aphasia, for example, suggests an additional degenerative pathology that likely will not improve with shunting.

Treatment consists of a neurosurgically placed shunt that drains cerebrospinal fluid into the peritoneal cavity. One of the known complications in the past has been overdrainage, which can cause the brain to shrink and may result in subdural hemorrhage or subdural hygroma. The recent introduction of programmable shunt valves, however, has improved outcomes and reduced the need for additional surgical procedures to adjust the rate of drainage.

NPH may have a degenerative component. Even in patients with initial success, it may be necessary to adjust the rate of drainage six months to several years later. The programmable valve readily enables such adjustments and has made surgery more viable for more patients.

Predicting cognitive outcomes

Not all symptoms improve with treatment. Often, gait and incontinence improve, but memory and cognition may not. Mayo neurologists suspect that overlapping conditions may be important to the cognitive decline associated with NPH. The presence of aphasia or even mild naming deficits may signal coexisting pathology, such as vascular disease or Alzheimer's disease (AD).

Studies have shown that among people older than 74 years, the brains of more than 30 percent of patients show evidence of AD pathology on autopsy. Cerebrovascular disease also is frequent in this age group because hypertension is common. Several studies show that hypertension is associated with hydrocephalus in animal models and with hydrocephalus in humans.

Related research

Mayo Clinic researchers analyzed data collected by the Atherosclerosis Risk in Communities (ARIC) Study, a prospective epidemiologic study sponsored by the National Heart, Lung, and Blood Institute. Looking at the MRI scans of study participants taken 10 years apart, researchers found that both increased systolic BP and increased pulse pressure correlated with increased ventricle size.

In earlier research, Mayo investigators showed that head size also correlates with increased risk of NPH. Approximately 10 to 20 percent of people with NPH have a head size at or above the 98th percentile. Thus, it may be that people born with a large head have congenital hydrocephalus that becomes symptomatic as they age.

The question of the contribution of head size, vascular disease and underlying AD pathological factors is important to predicting outcomes for surgical shunting. To address these issues, Mayo researchers are initiating a prospective study in which 25 patients with NPH who have agreed to shunt surgery will undergo neuropsychological tests and PET imaging to screen for amyloid-beta protein (Aβ) plaque buildup before surgery. They will also have gait evaluation and neuropsychological testing at one-year follow-up.

The goal of the study is to determine whether the presence of Aβ in the brain influences cognitive outcomes from shunt surgery in NPH. The investigators hope their findings will help physicians in counseling patients about which symptoms may improve with a shunt and whether shunting is a good option.

Points to remember

Normal pressure hydrocephalus (NPH) is difficult to diagnose. After other causes have been ruled out, Mayo Clinic neurologists use a test that mimics a temporary shunt.

Treatment for NPH consists of a neurosurgically placed shunt that drains cerebrospinal fluid into the peritoneal cavity. Use of newer programmable shunt valves has improved outcomes and reduced the need for additional surgical procedures.

Not all symptoms associated with NPH improve with treatment. Often, gait and incontinence improve, but memory and cognition may not.

Mayo Clinic researchers are initiating a prospective study to determine whether the presence of amyloid in the brain influences cognitive outcomes from shunt surgery in NPH.

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